Central Fatigue

Question 1

Lepers et al (2002)

Answer 1

• 9 trained participants cycling at 55% VO2max for 5 hours
• Measured MVC every hour
• Contractile changes occurred during the start of exercise (peripheral), however reduced MVC later in the exercise (central)

Question 2

Millet et al (2002)

Answer 2

• Assessed pre and post 60km ultra-marathon run
• Assessed voluntary activation (VA) by electrically imposed twitches (above MVC)
• 27% reduction in VA pre/post run
• Unsure why

Question 3

Ross et al, (2010)

Answer 3

• Simulated the Tour de France (20on/22)
• Assessed MVC and VA on rest days; 9 and 17 and 2 days following the trial
• Gradual reduction in VA and MVC throughout trial, VA was still reduced 2 days following
• Currently don’t know where central fatigue is coming from

Question 4

Amann and Dempsey, (2008)

Answer 4

• 2 constant load exercise bouts to exhaustion; at either 83% Wpeak or 67% Wpeak
• 83% group suffered more peripheral fatigue
• Subjects followed exhaustive bouts with 5km TT 4-mins later
• 83% group suffered reduced CMD and reduced power output
• All groups reached the same level of peripheral fatigue, however the 83% group had already reached it after the exhaustive bout
• It is suggested that each person have a critical peripheral fatigue threshold, and that 83% group had already achieved this threshold after exhaustive bout and therefore had to reduce CMD to avoid further peripheral fatigue, possibly via afferent feedback

Question 5

Amann et al (2008)

Answer 5

• Injected an epidural of lidocaine into the lumbar spine to stop the afferent feedback
• Same protocol
• 22% reduction in power output in epidural group
• However, 9% increase in iEMG
• The epidural stopped some effent feedback as well as afferent, therefore reduced power output, however the increase in iEMG suggests afferent feedback is involved in central fatigue

Question 6

Amann et al (2009)

Answer 6

• Used fentanyl to prevent afferent feedback but allow efferent feedback
• Same results as previous study
• However, efferent feedback hasn’t prevent power output
• CMD greater in Fent group

Question 7

Sidhu et al, (2014)

Answer 7

• Fentanyl study
• Measured arm exercise (non-active limb) during cycling
• Increased MVC, MEPs and VA in Fent group and decreased SIT in control group
• Due to the arm being a non-acid limb, yet still fatiguing mean it can be due to peripheral fatigue as there is no contractile work, therefore must be central fatigue

Question 8

Mauger et al (2010)

Answer 8

• 13 trained cyclists, 10-mile (16km) TT with/without Acetaminophen (ACT)
• Increased power output with ACT
• No difference in physiology (HR, RER, BLa)
• No difference in RPE or pain perception

Question 9

Foster et al (2014)

Answer 9

• 9 males performed 8 x WAnT (wingate) operated by 2mins with/without ACT
• Mean power significantly greater (9%) in sprints 6, 7, and 8 with ACT

Question 10

Amann et al (2006)

Answer 10

• 5km TT, 4 conditions; hyperoxia, isoxia, normoxia and hypoxia (blind)
• Reduced CMD and near stimulation positively correlated with reduced oxygen
• Peripheral fatigue same between conditions
• Lower iEMG in first 60s of exercise - before any homeostatic stress
• Critical peripheral threshold can’t explain the immediate down regulation in iEMG (central governor)

Question 11

Crewe et al (2008)

Answer 11

• 7 participants cycled until exhaustion at varying power outputs at either; 15°C or 35°C
• 70% of trial variation explained by rate of increase in RPE
• The rate of increase was the same between all conditions and decided in the first 30% of exercise
• RPE was higher before the start of exercise in hot condition compared to cool
• Central governor used telioanticipation to predict how hard exercise to be and therefore when to becomes fatigued

Question 12

Paterson and Marino (2004)

Answer 12

• Untrained cyclists - all told they were cycling 3x30km
• For group 1, trial 2 was 36km and for group 2, trial 2 was 24km
• Trial 3 was cycled faster by group 1 and slowed by group 2
• Central governor you anticipatory telioanticipation to predict how long the TT would be, based on the previous manipulated exercise

Question 13

What is the Central Governor model - Noakes (2011)

Answer 13

1. The body applies pacing before an event based on the perception of effort they think will have to be used. Pacing is to preserve homeostasis.
2. Pacing strategy is employed by sensory information on the periphery.
3. Pacing is purely sensory anticipation, therefore fatigue may be due to central neural efforts to maintain homeostasis
4. Role of the brain to to ensure exhaustion exists while homeostasis is maintained.